For example, partial discharges occur in equipment used in the high tension installations of networks for transporting and distributing electrical power. In a sequence of dielectrics subjected to high tension, one item is the seat of a breakdown, and the energy corresponding to the capacitive charge of said item is dissipated in the form of high frequency oscillation. The other items in the sequence retain their integrity, so the partial discharge does not lead to overall breakdown.
A study of partial discharges can be used to evaluate the quality of a piece of equipment and to provide useful information when quality is to be improved. It is therefore important to be able to perform measurements relating to partial discharges. Special measuring apparatuses have been developed for this purpose. By way of example, mention may be made of measurement system 9100 provided by the firm "Tettex AG" and described in the publication "Tettex Instruments-Information", No. 21, April 1987. Such apparatus performs measurement on current and voltage pulses produced by partial discharges and it displays the maximum values observed. Individual pulses may also be observed by means of an oscilloscope. In addition, the repetition of partial discharges is also significant. In communication No. 15-12, entitled (in translation) "Search for correlation between the energy of partial discharges and the degradation of paper/oil insulation", by F. Viale et al., given to the 1982 session of the International Conference on Large Electricity Networks, mention is made of integrating the energy of partial discharges over a given period.
The article "Simultane Erfassung und Verarbeitung von Teilentladungs-Kenngrossen zur Beurteilung elektrischer Isolierungen" by F. H. Kreuger et al., describes a system in which a microcomputer receives various digital values relating to each instant of a single partial discharge. The article deals with measures to be taken for reducing the volume of information to be stored and it even mentions conserving the time conditions of the recorded signals, but without proposing any solution.
Patent document DE-36 12 234 describes a system of the same type.
U.S. Pat. No. 4,757,263 describes apparatus for monitoring various electrical magnitudes in a single installation, however these magnitudes are basically continuous in nature, unlike the signals generated by partial discharges which are pulse signals and unpredictable.
Observing partial discharges at a plurality of points gives rise to the problem of recording a huge quantity of information continuously or quasi-continuously, unless observation periods are selected arbitrarily, in which case there is a danger of missing useful observations, or unless the results of the observations are treated which is expensive in treatment means. None of these solutions is satisfactory. In practice this prevents an experimenter from having a complete picture of discharge activities, and leaves it to the experimenter's experience or skill in selecting discharges that are particularly significant. However, there are numerous cases when it would be desirable to obtain fuller information on partial discharges, particularly during studies bearing on the correlation between the discharges and the deterioration of the equipment in which they take place. Although the energy of a partial discharge is indeed a measure of its harmfulness, it is also necessary to know what type of discharge is involved, i.e. where it has taken place. This may be deduced from observations made simultaneously at several points, for example.
A particular object of the present invention is to provide a system for measuring partial discharges and satisfying this requirement.